rroll is an open source (GNU GPL v3) Arduino project that uses an ultrasonic sensor to unleash cheesy music on unsuspecting passersby. Whenever someone enters within 6 feet of the sensor, the device is activated and starts playing Rick Astley's Never Gonna Give You Up. When the person leaves the area, the music pauses, only to resume where it left off when the person re-enters the area.
If you've never heard of it before, a Rickroll is a bait-and-switch Internet phenomenon where someone will post an interesting or shocking headline designed to catch people's attention, only to play Rick Astley's Never Gonna Give You Up when the unsuspecting visitor clicks the link. If you'd like to experience a traditional Rickroll, check out this one.
The device is powered entirely off of batteries so it can be hidden in the most obscure of places. I hot glued the components into place inside the casing to make a semi-permanent device. This will allow it to be jostled around without falling apart.
I will admit that I had already owned most of the parts and tools from previous projects before I started working on rroll. If I had to buy all of the parts just for this project, I probably wouldn't have done it. But maybe you just really want to Rickroll someone, so here are the complete part and tool listings: